Method for making wire drawing dies



Ap 6, 1937. G. F. TAYLOR; 9753 METHOD FOR MAKING WIREDRAWING DIES I Filed Jan. 29, 1932 Inventov George E Tqglow,

' His Attonn e q.

Patented Apr. 6, 1937 UNITED STATES 2,076,356 METHOD FOR WIRE DRAWING George F. Taylor, Niskaynna, N. assignor to General Electric Company, Y a

New York corporation of Application January'29, 1932,. Serial No. 589,755

' 6 Claims.

sired exterior shape by pressing a powdered mixture of a refractory carbide and binder element therefor, for example about 94% tungsten carbide and 6% cobalt, in a steel mold and under pressure of about -30. tons per square inch. 15 The exterior shape of the pressed material was made slightly conical to. permit easy removal from the mold. The shaped mass was sintered together at a temperature of about 900 C. for one-half hour to give it sufficient strength to 0 permit handling. An opening was then drilled along the axis of the nib. The latter operation was accomplished by means of steel twist drills. Since cemented carbide is very hard material, even when sintered at a temperature as low as 900 C., the drilling operation was slow and the drills lost their edge quickly thereby necessitating frequent resharpening.

After the drilling operation the nib was usually sintered in a hydrogen atmosphere for about 1% hours at 1400 C. This-latter treatment formed the nib into an extremely hard product ready to be mounted in the die-holder. The latter was provided with a central opening of slightly greater diameter than the nib, the lower part of the opening being contracted to form a ledge or support for the nib. The nib was placed on the ledge and surrounded by a quantity of copper suflicient to substantially fill the gap between the nib and holder. The die was then placed in a hydrogen furnace and heated to about 1100 C.

to braze the nib to the die-holder. Thereafter the die was removed from the furnace and placed in a lapping machine. By means of a mixture of abrasive materials and oils and the use of forming tools having suitable angles, the axial opening through the die was gradually worn away to a shape suitable for'wire drawing purposes.

The prior process of manufacturing cemented carbide dies is a long one and must be carried out by experienced operators having special skill since the dimensions and contour of the opening through the die must be minutely accurate. Furthermore, it is not unusual to wear out several forming tools in providing the proper shaped opening through each die, the forming tools usually being made of relatively soft material such as iron.

It is oneof the objects of the present invention to provide a simple, cheap and efficient process for manufacturing wire drawing dies'from powdered materials and particularly from powdered materials consisting of a refractory carbide and a binder metal therefor. Other objects of the invention will appear hereinafter.

The novel features which 'are characteristic of the present invention are set forth with particularity in the appended claims. The inventionv itself however will best be understood from reference to the following specification when considered in connection with the accompanying drawing in which Fig. 1 represents a view partly in section and partly in elevation of an apparatus whereby my invention may .be carried into eifect; Fig. 2 is a view partly in section and partly in elevation of a portion of the mold disclosed in Fig. 1; Fig. 3 is a cross sectional view o a wire drawing die formed in accordance with the present invention; Fig. 4 is a cross sectional view of a modification .ofa portion of the apparatus disclosed in Fig. 2. Fig. 5 is a perspective view partly broken away of a modified form of apparatus which may be employed in carrying out my invention, while Figs. 6, 7, 8 and 9 are cross sectional views of a portion of a carbon mold disclosing successive steps employed in manufacturing both a dieholder and die nib from powdered materials.

Referring more particularly to the drawing, I have indicated at H) and l l a pair of graphite bloclm each provided with cooperating semi-circular openings extending longitudinally therethrough to provide a cylindrical opening adapted to accommodate a mold designated as a whole by the numeral I2. The mold l2 comprises a hollow cylindrical metal, die-holder l3 and a hollow graphite cylinder 14 the external and internal diameters of which are equal respectively to the external and internal diameters of the die-holder IS. A graphite plug or core member l5 closes the lower portion of the die-holder l3. The core I5 is provided with a stem l6 whichis curved adjacent its lower end to have the exact contour of the "opening desired, in the die nib. Stem l6 is long enough to extend completelythrough the die-holder l3 and is enlarged at its lower end to provide a short cylindrical portion I! having substantially the same diameter as the internal diameter of the die-holder l3.

In fabricating the, die nib, the die-holder l3, graphite cylinder H and core I 5 are assembled as central longitudinal opening therethrough to accommodate stem I6 is then positioned in the cylinder l4 to apply pressure to the powdered mixture l8. The assembled mold is then placed between the carbon blocks l and II as indicated in Fig. 1. An electric current is supplied to the mold through a pair of water cooled terminals 20 and 2i connected to a suitable source of electrio current supply. A current is employed which is sufiicient to heat the powdered mixture l8 to its sintering temperature which in general is above 1000 C. With the apparatus disclosed the temperature of the powdered material cannot be observed directly but may be determined approximately from the temperature of the die-holder 13. For this purpose each of the blocks l0 and H is provided with a semi-circular opening 22 which openings cooperate to form a circular opening through which the temperature of the die-holder may be read directly with an optical pyrometer.

" As the powdered mixture is heated, pressure is simultaneously applied thereto through the graphite plunger l9 to thereby compress the powdered mixture l8 into a hard dense mass substantially free from voids. The pressure and heat are supplied for a few' minutes only. During this time the powdered material comprising the nib becomes securely welded to the die-holder I3. After the sintering operation is completed the mold is taken apart and the die, after a simple polishing operation on the nib, is ready for use.

It is particularly desirable in a wire drawing die that the nib portion be non-porous and free from voids. This may be accomplished by employing graphite plunger l9, as heretofore pointed out, to compress the powdered mixture while it is heated at its sintering temperature. If, however, it is desired -to insure the production of an extremely dense product this may be accomplished by employing higher pressures than may be employed with. a carbon plunger. Under such circumstances the plunger I! may be made of molybdenum, tungsten or any hard and refractory material such as quartz, alumina, magnesia, etc. When a metal plunger is employed it is necessary to prevent the plunger from becoming welded to the sintered material. This may be done by inserting a thin disc of fine grade carborundum paper between the powdered material and the plunger.

It is preferable to apply initially a gentle pressure to the powdered materials to prevent rupture of the graphite cylinder ll. Assoon how-' ever as plunger I9 has entered the opening in the die-holder I! the graphite cylinder ll merely serves as a guide for the plunger l8 and great pressures can thereafter be applied to the heated materials since the force tending to rupture the mold is then applied directly to the metal dieholder l3.

After the die has been in use for some time and the nib has worn away so that the opening therethrough is too large it can be shrunk to asmaller size by placing the die between the graphite core l and graphite plunger 19, inserting the. assembled members between blocks II and II and applying pressure to the die nib by means of the plunger I! while the nib is heated to a tempera ture above-1000 C.

Although I have illustrated my invention in connection with tungsten carbide and cobalt the invention is not limited to these materials.

A Other refractory carbides, for example molybdenum carbide, tantalum carbide or columbium carbide or mixtures of carbides may be substituted for tungsten carbide. Furthermore other binder metals having a lower melting point than the carbide employed therewith, for example nickel or iron, or metals of the iron group in combination with metals such as molybdenum,

tungsten, chromium or aluminum, may be 'substituted. for cobalt.

nection with a die having a circular opening therethrough. My invention however is not limited to dies having this particular opening. In accordance with my invention, dies with square, hexagonal or other shapes may be formed readily by employing a graphite or quartz core, corresponding to core I5, and shaped to have the contour desired in the finished die nib.

The graphite core I5 disclosed in Fig. 2 is made in one piece. In certain cases however, where the diameter of the opening through the nib to be fabricated is very small, for example about 60 mils or less, it may be desirable to form the stem portion of the core from quartz. A core of this character is disclosed in Fig. 4 in which a quartz stem 23 extends through the core I5 and cooperates with the lower curved portion 9 of the stem portion thereof.

The die-holder i3 is preferably made of molybdenum or an alloy thereof and may be fabricated in several ways. It may for example be made from a sintered bar. The latter may be,

swaged into a round shape and cut into portions having the desired thickness. These portions are then drilled to provide a ring-shaped structure such'as shown at It in Figs. 2 and 3. I prefer to form the die-holder from powdered molybdenum or a mixture of powdered molybdenum with other metal. This may be accomplished with the apparatus disclosed in Figs. 5-9 inclusive. In these figures I have disclosed a split graphite mold 24 the opposite contacting portions of the mold being provided with semi-circular openings which cooperate to provide a central openingin which hollow cylindrical graphite plungers 25 and 26 may be inserted.

In manufacturing the die-holder l3 from pow-v contact with the powdered material. Pressure is then applied to the hollow plungers 25 and 26 by means of movable pressure members 29 and 30 indicated in Fig. 5. At the same time that pres-- sure is applied to the powdered material an electric current of sufllcient intensity to sinter the powdered material is supplied to the carbon mold through water cooled terminals 3| and 32.

When the powdered material has been pressed and sintered as indicated in Fig. '1 the assembled plungers 25 and 26 and rod 21 are removed i'rom the mold 24 and the rod 21 pushed out of the plungers 25, 26 and die-holder 22. A graphite plug or core 33, similar to core I! and the upper en'd of which has a projecting stem 24, is then inserted through the graphite cylinder 28 and the sintered die-holder 28. The lower end of the projecting stem 24 is shaped to have a contour similar to that desired in the finished die nib.

, Powdered material 35, which may be a mixture of tungsten carbide and cobalt or other suitable material, is now inserted on top of plug 33 and around stem 34 and a plunger 36 inserted in the graphite cylinder 25. The assembled cylinders and die-holder and powdered material are then placed within the mold 24 and pressure applied to the plunger 36 while the powdered material 35 is simultaneously heated to its sintering temperature by means of current supplied through the terminals 3i and 32. I

When the die-holder is made from powdered material, it is not only possible to carry out the manufacturing operation quickly and efflciently but there is an added advantage in that the dieholder may be made from combinations of various powdered materials which will provide a dieholder having substantially the same coeidicient of expansion as the nib portion of the die. For example, a die-holder consisting of molybdenum and tungsten may be employed with a die nib having a composition of about 87% tungsten I formed exactly so that very little lapping is necessary to prepare the die for wire drawing' tungsten carbide and 6% cobalt. The 13% cobalt composition has a coeflicient of expansion slightly higher than that of molybdenum while the 6% cobalt composition has a coefllcient slightly below that of molybdenum. The addition to the molybdenum of a suitable amount of tungsten powder, which has a coefficient of expansion below either of the above compositions of tungsten carbide and cobalt, would give any desired coefficient between these two extremes. This is particularly important since the die nib may crack at the boundary betwen the nib and dieholder unless the coefllcient of expansion of the two .are substantially identical.

A die made in accordance with my process has several advantages, for example a great saving may be eilfected in the time required to make the die due to the elimination of many operations heretofore necessary in the fabrication of cemented carbide wire drawing dies. Furthermore theangular contour of the die nib maybe operations. The hole through the nib is exactly concentric and coaxial with the holder and the nib is made an integral part of the holder so that copper brazing or shrinking. is not necessary.

Moreover, the nib does not require a supporting ledge on the holder since it is integrally joined to the latter member,

What I claim as new and desire to secure by I 2. The method oi forming a wire drawing die comprising a die holder and nib which comprises compressing the powdered ingredients comprising said nib within said die holder and between a plunger and a non-metallic plug while said ingredients are heated to their sintering temper ature, said plug being provided with a central non-metallic stem extending through said die holder and having substantially the contour desired in'the finished nib and removing said plug member for one end of the die-holder and pressing a powdered composition positioned within said die-holder and around said stem while said composition is heated at a temperature above 1000 C.

4. The method of forming a wire drawing die comprising .a holder having a bore of substantially uniform diameter and a nib portion which comprises positioning a non-metallic plug in one.

end of said bore to form a closure therefor, said plug being provided with an upwardly extending stem having substantiallythe contour desired in the finished nib, placing powdered material within said bore and on said plug, applying pres sure to said powdered material, heating the pressed material to its sintering temperature,

and removing said plug from the sintered nib.

5. The method of forming a wire drawing die comprising a holder having a bore of substantially uniform diameter and a nib portion which comprises positioning a non-metallic plug in one end of said bore to form a closure therefor, said I plug being provided with an upwardly extending stem having substantially the contour desired in the finished nib. placing powdered material within said bore and on said plug, heating said holder 7 and powdered material to an elevated temperature, simultaneously applying pressure to the powdered material only to thereby weld it to said holder, and then removing said plug. v

6. The method of forming a .wire drawing di comprising a molybdenum holder having abore of uniform diameter and a cemented carbide nib portion which comprises positioning a nonmetallic plug in one end of said bore to form a closure therefor, said plug being provided with an upwardly extending stem having substantially the contour desired in the finished nib, placing mixed powdered ingredients comprising said cemented carbide nib within said bore and on said plug, simultaneously applying heat and pressure to said mixed powdered ingredients to simultaneously sinter. the mixture and weld it to said holder, and removing said plug from the sintered nib.

GEORGE F. TAYLOR. 

